Tunable lenses are optical elements whose optical characteristics, such as the focal length and/or the location of the optical axis, can be adjusted during use, typically under electronic control. Such lenses may be used in a wide variety of applications. For example, U.S. Pat. No. 7,475,985 describes the use of an electro-active lens for the purpose of vision correction.
Electrically-tunable lenses typically contain a thin layer of a suitable electro-optical material, i.e., a material whose local effective index of refraction changes as a function of the voltage applied across the material. An electrode or array of electrodes is used to apply the desired voltages in order to locally adjust the refractive index to the desired value. Liquid crystals are the electro-optical material that is most commonly used for this purpose (wherein the applied voltage rotates the molecules, which changes the axis of birefringence and thus changes the effective refractive index), but other materials, such as polymer gels, with similar electro-optical properties can alternatively be used for this purpose.
Some tunable lens designs use an electrode array to define a grid of pixels in the liquid crystal, similar to the sort of pixel grid used in liquid-crystal displays. The refractive indices of the individual pixels may be electrically controlled to give a desired phase modulation profile. (The term “phase modulation profile” is used in the present description and in the claims to mean the distribution of the local phase shifts that are applied to light passing through the layer as the result of the locally-variable effective refractive index over the area of the electro-optical layer of the tunable lens.) Lenses using grid arrays of this sort are described, for example, in the above-mentioned U.S. Pat. No. 7,475,985.
PCT International Publication WO 2014/049577, whose disclosure is incorporated herein by reference, describes an optical device comprising an electro-optical layer, having an effective local index of refraction at any given location within an active area of the electro-optical layer that is determined by a voltage waveform applied across the electro-optical layer at the location. An array of excitation electrodes, including parallel conductive stripes extending over the active area, is disposed over one or both sides of the electro-optical layer. Control circuitry applies respective control voltage waveforms to the excitation electrodes and is configured to concurrently modify the respective control voltage waveforms applied to excitation electrodes so as to generate a specified phase modulation profile in the electro-optical layer.
U.S. Patent Application Publication 2012/0133891 describes an electro-optical apparatus and method for correcting myopia that includes at least one adaptive lens, a power source, and an eye tracker. The eye tracker includes an image sensor and a processor operatively connected to the adaptive lens and the image sensor. The processor is configured to receive electrical signals from the image sensor and to control the correction power of the adaptive lens to correct myopia, with the correction power dependent on a user's gaze distance and myopia prescription strength.